1. Field of the Invention
The present invention relates to a variable magnification optical system and, for example, to a variable magnification optical system suitable for a digital camera, a video camera, a digital device with image input function, and the like capable of acquiring an image of a photographic object through an image sensor. In particular, the present invention relates to a small zoom lens system suitable for a barrel retraction type. The present invention further relates to an imaging device employing a variable magnification optical system.
2. Description of the Related Art
In recent years, size reduction is progressing in digital cameras and video cameras. Thus, size reduction and thickness reduction are desired in imaging devices employed in these cameras. Further, demand is also increasing for compact imaging devices capable of being installed on digital devices such as a portable phone and a personal information terminal. Thus, in the prior art, various types of zoom lens systems have been proposed in order to satisfy such desire. For example, in zoom lens systems described in Patent Documents 1 and 2, the number of lenses and the thickness of each lens group are reduced so that the thickness is reduced at the time of barrel retraction. As a result, the camera size is reduced at the time of lens accommodation. In zoom lens system described in Patent Document 3, one of lens groups escapes from the optical axis at the time of barrel retraction so that the thickness reduction is achieved in the camera.
[Patent Document 1] U.S. Pat. No. 6,943,962B2
[Patent Document 2] U.S. Pat. No. 7,046,452B2
[Patent Document 3] U.S. Pat. No. 6,978,088B2
In the zoom lens systems proposed in Patent Documents 1 and 2, although the camera thickness is suppressed at the time of lens accommodation, the overall lens length in the image shooting state becomes long. This causes complexity in the mechanical configuration for moving the most object side lens group to the image shooting state position. In the zoom lens system proposed in Patent Document 3, the lens barrel thickness at the time of barrel retraction is reduced further by virtue of the employed escape technique. This causes further difficulty in the draw-out of the lens at the time of image shooting.
The present invention has been devised in view of such situations. An object of the present invention is to provide: a variable magnification optical system in which reduction of the thickness in a retracted state and reduction of the overall lens length in the image shooting state are achieved with maintaining satisfactory optical performance; and an imaging device employing this variable magnification optical system.